First thing to check is refrigerant amount in system (check in owners manual as can't remember at present), also make sure it has had either Denso ND11 A/C Compressor Oil or Hybrid Electric Vehicle A/C Compressor Oil Used, as these are not electrically conductive, whereas normal A/C compressor oil is and can damage the compressor/ short it out if put into the system.
From my experience with A/C Leaks on the (MHU38) RX400h's the 3 main/ common points where they suffer from A/C leaks is
The A/C Condenser Radiator (stone/ debris impacts) due to exposure/ little protection behind the bumper.
Also there is a silver 10mm diameter A/C pipe (can't remeber if High or Low pressure A/C) located behind the front bumper metal crash bar (
when viewed from up underneath through bumper grille under Front No. Plate area. Leak visible on pipe area infront of A/C Condensor Radiator) that is prone for leaking due to debris impacts and poss cracking. This pipe runs along the front (as mentioned) and along passenger side of Engine bay over the Hybrid CVT transmission.
Have known of another leak area on the above mentioned pipe (only noticeable with dye and UV lamp) from above the Hybrid CVT Transmission/ next to N/S Chassis leg visible through N/S/F Wheel arch. both leaks can be noticed from the oily and dirty residue on the pipes and condenser radiator.
If the above mentioned pipe is leaking can be a 5hour labour approx job as N/S Headlamp, Front Bumper, N/S/F Engine bay Fuse Box, and Hybrid Inverter (not the gearbox but the unit mounted on top with the coolant bottle next to it ) require removal and refitting.
I would only recommend a Reputable Lexus Dealer to carry the replacement of the mentioned pipe out, as not a job for an amateur mechanic due to involvement with the Hybrid electric system.
Apologies for the long read, but all I can remember/ think of for now lol!, hth.